1. Field of the Invention
This invention relates to a laser processing method for a wafer for processing a wafer such as a semiconductor wafer or an optical device wafer using a laser beam.
2. Description of the Related Art
A wafer such as a silicon wafer or a sapphire wafer having a plurality of devices such as ICs, LSIs or LEDs formed on a surface thereof partitioned by scheduled division lines is divided into individual devices by a processing apparatus, and the divided devices are utilized widely in various electric apparatus such as portable telephone sets or personal computers. For the division of a wafer, a dicing method which uses a cutting apparatus called dicer is adopted widely. In the dicing method, a cutting blade of a thickness of approximately 30 μm formed from abrasive grain of diamond or the like solidified with metal or resin is rotated at a speed as high as approximately 30,000 rpm while being moved to cut into a wafer to cut and divide the wafer into individual devices.
Meanwhile, in recent years, a method has been proposed in which a pulse laser beam of a wavelength with regard to which a wafer has absorbency is irradiated upon the wafer to form laser processing grooves (dividing grooves) and external force is applied to the wafer along the laser processing grooves by a breaking apparatus to divide the wafer into individual devices (refer to, for example, Japanese Patent Laid-Open No. Hei 10-305420). By the formation of laser processing grooves by the laser processing apparatus, the processing speed can be increased in comparison with the dicing method by a dicer and even a wafer made of a material having a high hardness such as sapphire or SiC can be processed comparatively readily. Further, since the processing grooves can be formed with a small width of, for example, 10 μm or less, the number of devices to be taken per one wafer can be increased in comparison with the case in which the dicing method is used for processing.
In processing of a wafer by a laser processing apparatus, a wafer is adhered to a dicing tape which is adhered at an outer peripheral portion thereof to an annular frame such that the wafer is supported on the annular frame through the dicing tape. Then, a laser beam is irradiated upon the wafer in a state in which the wafer is sucked to and held by a chuck table of the laser processing apparatus through the dicing tape.